RasPi as subnet router

Trying to set up a raspberrypi as a subnet router to conect to an ESP32.
following the TS guide :
pi@Pi4B8:~ $ sudo tailscale up --advertise-routes=
“” is not a valid IP address or CIDR prefix

what does the error message mean?
what does /24 after the ip address mean ( it makes no difference to the error msg)

Excuse the newbie question

It just means its part of a /24 subnet which is 192.168.1.X where x is 1 through 255. You would use this if you wanted to subnet route the entire 192.168.1.x subnet.

If you just want to route a single IP, you could do

/32 means a single host only.

Thanks that worked fine.
What does /24 mean? Since it got rejected before.

/24 is the subnet, the IP you’re trying to route isnt a /24 subnet so it wont work, as above if you just want to route to 1 ip, use /32 which is the subnet for a single address